Auditory brainstem responses and electroencephalographic findings in patients with occupational vibration disease

To evaluate the function of the central nervous system of patients with occupational vibration disease, electroencephalograms and auditory brainstem responses (ABR) were recorded in 20 male subjects with occupational vibration disease whose age ranged from 46 to 67 years (mean 57.4 yr). All the subjects had operated chain saws from 10 to 25 yr (mean 15.2 yr) and had frequently complained of many subjective symptoms induced by central nervous system disturbances such as headache, head heaviness, tinnitus, vertigo, and insomnia, which corresponded to stage 3 in the diagnostic criteria of Andreeva-Galanina. Twenty-six healthy men whose age ranged from 40 to 67 yr (mean 53.0 yr) were selected as controls. Electroencephalograms were recorded with a 12-channel electroencephalograph, using unipolar and bipolar leads. Auditory brainstem responses were recorded by signal averaging technique using 100 μs alternating clicks. The stimuli were presented at 70 dB above threshold (SL) with a rate of 10 per second. The following results were obtained.1. By electroencephalography, the incidence of diffuse alpha pattern, slow alpha wave and drowsy pattern was 32%, 32%, and 42%, respectively.2. Click thresholds in the patients were obviously higher than those in the healthy controls.3. The occurrence rate of wave II of ABR in the patients (61.8%) was significantly lower than that in the healthy controls (85.0%) (p<0.05).4. The interpeak latencies I-V and III-V of ABR in the patients were significantly longer than those in the healthy controls. These findings suggest that the conduction velocity of brainstem auditory tract is reduced in the patients.5. In the patients, the peak latencies and interpeak latencies of ABR waves were negatively correlated with the click thresholds. Therefore, delay in the interpeak latencies I-V and III-V does not indicate the severity of hearing impairment.6. The interpeak latencies I-V and III-V in patients who always complained of tinnitus were significantly longer than in those who sometimes complained of tinnitus or did not at all. Thus a close relationship between delay of interpeak latencies and severity of tinnitus was suggested.These findings suggest that these examinations are useful in evaluating the function of the central nervous system in patients with occupational vibration disease.